1. Field of the Invention
The present invention relates to a wall flow type exhaust gas purification filter. More specifically, the present invention relates to a wall flow type exhaust gas purification filter suitably used for purifying particulate matter, nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) contained in exhaust gas from automobile engines.
Reduction of fuel consumption of automobiles has been demanded in recent years from the viewpoints of influence on the global environment and resource saving. Therefore, internal combustion engines having good heat efficiency such as a diesel engine and a direct-injection gasoline engine tend to be used as a power source for an automobile.
On the other hand, such internal combustion engines have a problem of soot generation upon combustion. From the viewpoint of the atmospheric environment, a measure not to release the aforementioned particulate matter such as soot to atmosphere is necessary.
As a measure not to release the aforementioned particulate matter to atmosphere, there has been proposed removal of particulate matter in exhaust gas by the use of an exhaust gas purification filter. As an exhaust gas purification filter, for example, there can be mentioned a wall flow type exhaust gas purification filter provided with a honeycomb structure having porous partition walls separating and forming a plurality of cells extending from one side end portion to the other side end portion and functioning as exhaust gas passages and plugging portions for alternately plugging one side end portion and the other side end portion of each of the cells of the honeycomb structure.
2. Description of Related Art
JP-A-2007-501353 discloses a means for filling a catalyst into pores of the partition walls of the wall flow type exhaust gas purification filter.
Purification with a wall flow type exhaust gas purification filter having a selective reduction (SCR) catalyst loaded thereon is effective for purifying NOx and particulate matter discharged from diesel engines. However, when a catalyst is loaded on a wall flow type exhaust gas purification filter where both the end portions are alternately plugged, gas permeability of the partition walls is degraded, which causes a problem of increase in pressure loss.
In addition, as a means for removing particulate matter discharged from a direct-injection gasoline engine, NOx, CO, and HC at the same time, it is effective to load a ternary catalyst on a wall flow type exhaust gas purification filter. However, there arises a problem of increase in pressure loss due to degradation of the gas permeability of the partition walls by the loading of the catalyst. Further, in a conventional technique where a SCR catalyst is coated on the partition walls of a honeycomb structure, there arises a problem of increase in pressure loss due to reduction of the opening ratio by the thickness of the catalyst coat layer.